1. Field of the Invention
The present invention relates to improving images and more particularly to object localization with an advanced search hierarchy.
2. Description of the Prior Art
The needs for accurate and efficient object localization prevail in many industrial applications, such as automated visual inspection and factory automation. The efficiency of the object localization system is directly related to the throughput of the product. In addition, the machine vision system should also be general enough to perform different kinds of tasks in a very short period of task switching time. This can significantly increase the applicability as well as the productivity of the system, which is very important for adapting to the fast changing needs of customers and markets.
The image reference approach is very popular in automatic visual inspection due to its general applicability to a variety of inspection tasks. This is further described by R. T. Chin in xe2x80x9cAutomatic Visual Inspection: 1981 to 1987xe2x80x9d, Computer Vision, Graphics, and Image Processing, Vol. 41, No. 3, pp. 346-381, 1988. However, it requires very precise alignment of the inspection pattern in the image. To achieve very precise pattern alignment, traditional template matching is extremely time-consuming when the search space is large. Some methods have been proposed to resolve this alignment problem. These are described by T. S. Newman and A. K. Jain in xe2x80x9cA Survey Of Automatic Visual Inspectionxe2x80x9d, Computer Vision and Image Understanding, Vol. 61, No. 2, pp. 231-262, 1995; by A. A. Rodriguez and J. R. Mandeville in xe2x80x9cImage Registration For Automated Inspection Of Printed Circuit Patterns Using CAD Reference Dataxe2x80x9d, Machine Vision and Applications, Vol. 6, pp. 233-242, 1993; and by T. Hiroi, S. Maeda, H. Kubota, K. Watanabe and Y. Nakagawa in xe2x80x9cPrecise Visual Inspection For LSI Wafer Patterns Using Subpixel Image Alignmentxe2x80x9d, Proc. Second IEEE Workshop on Applications of Computer Vision, pp. 26-34, Florida, December 1994. Rodriguez and Mandeville proposed an image registration technique by fitting feature points in the zero-crossings extracted from the inspection image to the corresponding points extracted from the CAD model via an affine transformation. However, the correspondence between the two set of feature usually can not be reliably established. Hiroi et al. presented a sum-of-squared-differences (SSD) based method to determine the shift between the two images. Unfortunately, this method is restricted to recover small shifts.
The present invention provides a new FLASH (Fast Localization with Advanced Search Hierarchy) system for fast and accurate object localization in a large search space. This object localization system is very useful for applications in automated visual inspection and pick-and-place systems for automatic factory assembly. This system is based on the assumption that the surrounding regions of the pattern within the search range are always fixed. The FLASH system comprises a hierarchical nearest-neighbor search system and an optical-flow based energy minimization system. The hierarchical nearest-neighbor search system produces rough estimates of the transformation parameters for the optical-flow based energy minimization system which provides very accurate estimation results and associated confidence measures.